Questioning the paradigm of a phosphate-limited Archean Biosphere

Abstract

The nature of Archean life remains one of the most contested topics in the study of Earth history. The debate may be formulated as follows: When did present day metabolisms emerge to ecological significance? What limited the productivity of early biospheres? How did the existence and productivity of individual metabolisms affect the chemistry and oxidation state of the ocean‐atmosphere? In a new study, Ingalls et al. (2022, https://doi.org/10.1029/2022GL098100) apply a novel proxy, carbonate‐associated phosphate (CAP), to Neoarchean carbonate rocks and argue that seawater in the Neoarchean was more phosphate‐rich than through Phanerozoic time. Although the interpretation of CAP signals is currently burdened by uncertainties regarding Archean seawater chemistry, their results suggest Archean phosphate levels were comparable to modern seawater, if not higher. If true, then Earth's most successful metabolism, oxygenic photosynthesis, had either not achieved ecological prominence to exploit the relatively phosphate‐rich waters, or was curtailed by other under‐appreciated mechanisms.Plain Language SummaryOver geologic timescales, the nutrient phosphate is thought to set the overall limit on the size and productivity of Earth's biosphere. Whether this limitation was more severe in early Earth history has been the subject of intense debate. In a new study, Ingalls et al. (2022) argue that Neoarchean seawater was richer in phosphate than present‐day seawater. If correct, this discovery has important implications for the early history of life on Earth.Key PointsCarbonate‐associated phosphate measurements suggest that phosphate limitation of the Neoarchean biosphere was not more severe than todayIf oxygenic photosynthesis existed well before the Great Oxidation Event, the productivity of this metabolism was limited by other factorsCarbonate‐associated phosphate, alongside other carbonate‐based proxies, can inform seawater chemistry and the carbon cycle through time